Variability of thermospheric densities from satellite observations near dawn and dusk

The thermosphere is a layer of the atmosphere that extends from about 90 to 500 km. Understanding variations in thermospheric neutral densities is crucial for planning Low Earth Orbit satellite missions, as these neutrals cause disturbances in orbits through drag effects. Because the ionosphere is embedded in the thermosphere, gaining insight into the variability of thermospheric densities enhances our comprehension of the interconnected dynamics among the thermosphere, ionosphere, and lower atmosphere. In addition, the ionosphere affects technologies such as HF communications and GNSS positioning.

This study utilizes data from the Gravity field and steady-state Ocean Explorer (GOCE). The mission provided dawn and dusk neutral densities between about 220 km to 270 km of altitude, with variations in the height of the satellite within one orbit of about 20 km. Thermospheric neutral densities experience variations based on altitude, latitude, longitude, solar flux, geomagnetic conditions, seasons, and local time. In particular, they generally fall off exponentially with altitude, with scale heights varying from 25 to 75 km. Therefore, in order to investigate other variations, normalization of the densities to a reference altitude is necessary for the GOCE dataset, due to the significant height variations even within the same orbit. In this work, we normalize the observed densities to a reference altitude for both dawn and dusk in order to investigate their variability due to other factors.